FXUS65 KTFX 052345 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 445 PM MST Tue Mar 5 2024 ...Aviation Section Updated... .SYNOPSIS... The most active portion of weather over the upcoming week will be through Wednesday morning across Southwest Montana, where falling and blowing snow will be a concern near the Idaho border. Otherwise, expect a slow warming trend with mostly dry conditions through the weekend, though the warmer air will likely take a bit longer to arrive in cold prone valleys like the Milk River Valley. && .DISCUSSION... Through Wednesday morning... Embedded features within broad troughing will result in snow developing across Southwest Montana this afternoon and evening, primarily south of I-90. Dynamics aloft aren't overly impressive, though closer to the surface stronger 700 mb winds will result in both a concern for a band of snow developing via frontogenesis near the Idaho border, as well as blowing/drifting of snow in north south oriented valleys (Primarily the southern portions of the Madison River Valley) and over Idaho passes at and east of Monida Pass, through the evening. High resolution ensembles are highlighting now through about midnight as the most favorable time for the band of snow, but do not give more than around a 30% chance for inch per hour snowfall rates on major roadways away from West Yellowstone. The best opportunity for inch per hour snowfall rates will reside near West Yellowstone, where the probability is around 50% for the aforementioned timeframe. Winter Weather Advisories continue across areas near the Idaho border through early Wednesday morning, though most, if not all, impacts will be over by the time 5 AM rolls around Wednesday. Further north, the 12Z Raob from the office this morning shows a sharp inversion with temperatures rising to nearly 25 F at the top of the inversion around 800ft AGL. The challenge with this is determining how much warming will occur below the inversion at lower elevation locations across the plains. For example the Great Falls Airport warmed from near 10 degrees up into the mid 20's over ~ an hour late this morning. This type of warming should spread further out onto the plains this afternoon, but confidence that this will make it all the way north/east across the plains is low. Hence, I have kept temperatures across northeastern portions of the plains on the low side for the rest of today. A weak Canadian front drops south tonight, allowing for temperatures across most of the plains to fall into the single digits above/below zero. Wind chills along the Canadian border will likely approach -20 F in spots, but appears to be too localized to consider a wind chill advisory at this time. Wednesday into early next week... Upper level troughing begins to push off to the east Wednesday, but it will linger long enough to keep Wednesday on the cool side, with just a small chance for light snow across the eastern Hi-Line in the morning (Probability for a trace of snow is on the order of 40% in this area). Upper level ridging begins to build in off to the west Thursday, though a weak embedded disturbance will dive southeastward in the northwest flow aloft. Temperatures will begin to trend slightly upward, but not by much, especially in wind protected typical cold spots like the Milk River Valley. A more noticeable warming trend commences Friday, though again, locations prone to delayed warmups will likely hold onto colder temperatures a bit longer. Cluster guidance favors the ridge axis passing overhead sometime Saturday, which look to be the warmest day of the forecast period. Southwesterly flow aloft develops ahead of a building northeast Pacific trough as this ridge passes off to the east Sunday. Temperatures do not look to fall much as this transition takes place into early next week, but chances for precipitation, mainly in the mountains, will re-enter the forecast. -AM && .AVIATION... 445 PM MST Tue Mar 5 2024 (06/00Z TAF Period) For this TAF period VFR conditions prevail across the KBZN, KHLN, and KLWT terminals with light winds and mostly low- to mid-level clouds. For the KHVR and KCTB terminals there will be MVFR ceilings from about 05Z until about 15Z. During this time period there could also be fog reducing visibility at the KCTB and KHVR terminals. However, there wasn't enough probabilistic support to include it in those TAFs. Early Wednesday morning at the KHVR terminal there is a slight (20%) chance for snow. For the KGTF terminal from 12Z to 15Z there will MVFR ceilings. From now until 04Z there will be snow at KEKS terminal which will intermittently reduce visibility to MVFR levels. Additionally at KEKS terminal there will be MVFR ceilings from 03Z to 12Z. At the KBZN terminal there is the potential for fog and snow early Wednesday morning but the chance for snow (30%) and probabilistic guidance for fog weren't high enough to include in the TAF. At the beginning of this TAF period there will be mountain obscuration and mountain wave turbulence primarily in Southwestern Montana. -IG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 3 31 14 38 / 0 0 0 0 CTB -4 26 6 35 / 10 0 0 0 HLN 13 34 12 35 / 10 0 0 0 BZN 11 31 9 32 / 40 0 10 0 WYS 7 30 8 30 / 90 10 20 10 DLN 11 32 11 31 / 30 0 0 0 HVR 1 14 -2 24 / 40 20 0 0 LWT 8 28 10 34 / 20 0 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 5 AM MST Wednesday for Gallatin and Madison County Mountains and Centennial Mountains-Madison River Valley-Ruby Mountains and Southern Beaverhead Mountains. && $$ http://www.weather.gov/greatfalls